Concrete is one of the most ubiquitous materials found in the modern world. It is one of the primary materials used to build almost every durable structure, large or small, comprising our cities and towns, including: sidewalks; roads; bridges; retaining walls; skyscrapers; building foundations; sewers; and hundreds of other structures. In short, concrete is used in every corner of the Earth and our way of life depends on its continued use.
Although concrete can be made in many ways with many additives and various methods for its creation and use, it is generally made with four parts gravel, two parts sand, one part Portland cement and water. These ingredients are mixed, poured into forms and allowed to set. This process has been repeated thousands of times every day for decades and decades.
Unfortunately, the manufacture of concrete's constituent parts creates an enormous amount of environmental havoc, which must be addressed. Huge quantities of sand, limestone and gravel must be mined or dredged each year to satisfy the requirements of concrete manufacture. These processes scar the Earth and must be performed using large machines, which burn a tremendous amount of fossil fuels, which also contribute to global warming. However, the carbon dioxide created by these processes pales in comparison to that required to manufacture Portland cement. The manufacture of one pound of Portland cement creates almost one pound of carbon dioxide due mostly to the decarbonation of limestone and the fuel burned to heat kilns to the required temperature of nearly 1500 degrees Celsius. International studies have shown that the manufacture of concrete leads to 5-8% of total CO2 emitted worldwide.
To be more cost effective and to prevent excessive waste, concrete mixtures have been developed which use recycled materials to reduce any unnecessary environmental impacts. Recyclable materials exist in many manufacturing industries such as coal-generated electricity, various metal purification processes, silica production and cement and lime kilns to name a few. These mixtures generally consist of either the addition of an aggregate mixture, made of recycled concrete or the addition of fibers, such as plant fibers, carpet fibers, or rubber fibers. The recyclable materials that can be used in the concrete mixtures exist in many manufacturing industries such as coal-generated electricity, various metal purification processes, silica production and cement and lime kilns to name a few.
What is needed is a concrete mixture that uses all of the commonly available types of recycled materials, thus requiring little or no Portland cement, and full recycled aggregate replacement to reduce landfill and destruction of our natural resources. Additionally, the concrete formed must have comparable strength, viscosity, and other characteristics comparable to that of standard concrete created from virgin materials.